1. Field of the Invention
This invention relates generally to valve trim assemblies for control valves or the like.
2. Description of the Prior Art
It is well known that control valves, particularly those which are employed to achieve high pressure drops, will suffer damage or wear to their internal parts. This damage may be caused for example by cavitation or by erosion. It is also well known that the stem packing in such a valve may become worn and begin to leak.
In the event that the valve trim or packing becomes worn or damaged, the valve must be disassembled and the worn or damaged parts replaced. Quite often, such disassembly and replacement must be accomplished quickly with a minimum of equipment, by personnel who may be unskilled in the adjustment of control valves for proper operation.
Heretofore, it has been common to provide, in a control valve, a valve seat which is retained in a valve body, and a valve bonnet in which a valve stem is slidably received, the bonnet being retained on the body by means of bolts or a threaded connection. The valve stem is provided at its interior end with a plug which seats against the valve seat for preventing or selectively regulating flow of fluid through the valve. The end of the valve stem which extends exteriorly of the valve bonnet is connected to a diagragm, and control air pressure acting on this diaphragm is used to vary the valve plug position. The connection of the valve stem to the diaphragm has been made in a number of ways, such as by screwing the outer end of the valve stem into a threaded connector which is affixed to the diaphragm assembly, but it has been necessary to make this connection in such a way that the valve stem cannot rotate, and thereby unscrew from the diaphragm, while the valve is in use. To prevent valve stem rotation, it has been common to employ a jam nut which must be screwed onto the threaded outer end of the valve stem, which is then screwed into a threaded connector affixed to the diaphragm. The jam nut is then screwed tightly against the connector to lock the valve stem against rotation.
In order to replace the trim in such a prior art valve, it has been necessary to employ special tools for installation of the valve seat in the valve body and for installation of the valve stem. Moreover, it has been necessary to use care in reinstalling the valve bonnet on the valve body to insure that the valve plug and valve seat are properly aligned and adjusted to insure proper stroke and tight shutoff.